JPH03492B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection control device for an internal combustion engine.

[Conventional technology and problems]

Conventionally, in engines that have fuel injection valves and are controlled by a microcomputer, in addition to fuel injection performed at every predetermined crank angle during normal operation (hereinafter referred to as synchronous injection), fuel injection is performed to improve starting performance at the time of starting. Injection (hereinafter referred to as asynchronous injection) is performed. This asynchronous injection is generally designed to supply a large amount of fuel corresponding to the amount of fuel required for full-load operation in cold conditions, and a very long injection time is set.

However, when starting an engine when the temperature of the fuel system is high, such as when the engine is stopped after high-output operation in the summer and then restarted soon, it is necessary to perform asynchronous injection in the same way as during a cold start. As mentioned above, in asynchronous injection, the fuel injection valve is open for a relatively long period of time, so the fuel pressure decreases within the fuel injection valve, causing boiling under reduced pressure, and vapor is generated within the fuel injection valve. There is.

When vapor is generated in this way, the bubble remains in the fuel injection valve for a while, and the amount of fuel corresponding to the opening time of the injection valve is not supplied. Therefore, in both asynchronous injection and synchronous injection, the amount of fuel injection is This will be lower than the calculated value. As a result, the air-fuel ratio immediately after a high-temperature start becomes too lean, which may cause rough idling or engine stall.

Note that Japanese Patent Application Laid-Open No. 58-25533 discloses a configuration in which the fuel injection time in asynchronous injection is shortened when the engine cooling water temperature is high, but this configuration does not completely eliminate the possibility of reduced pressure boiling mentioned above. It is not intended to be removed.

[Means for solving problems]

As shown in the configuration diagram of the invention in FIG. 1, the fuel injection control device according to the present invention includes a synchronous injection means 2 that causes the fuel injection valve 1 to perform an injection action at every predetermined crank angle during normal operation; When the engine is started, the asynchronous injection means 3 causes the fuel injection valve 1 to perform an injection action for a longer time than the fuel injection by the synchronous injection means 2, the state detection means 4 detects the engine state, and the state detection means 4 detects the fuel injection depending on the engine state. The present invention is characterized in that it includes a start control means 5 which controls the asynchronous injection means 3 not to perform an injection action when there is a possibility that boiling under reduced pressure may occur.

〔Example〕

The present invention will be explained below with reference to illustrated embodiments.

FIG. 2 shows an engine to which an embodiment of the present invention is applied. In this figure, an intake passage 11 is provided with a throttle valve 12 for controlling the amount of intake air. An air flow meter 13 for measuring the amount of intake air is installed upstream of the throttle valve 12, and an air flow meter 13 is installed downstream of the throttle valve 12.
A surge tank 14 is formed to suppress the influence of intake pulsation on the air.

The fuel injection valve 15 is provided on the downstream side of the intake passage 11, and injects fuel toward a head portion of the intake valve (not shown). Moreover, the fuel injection valve 15 is connected to the delivery pipe 1
6, and the natural material is fed under pressure to the delivery pipe 16 from a fuel pump (not shown) via a filter. The pressure regulator 17 is connected to the delivery pipe 16 and acts to keep the fuel pressure acting on the fuel injection valve 15 constant relative to the pressure in the intake passage 11. Excess fuel that is not injected by the fuel injection valve 15 passes through the pressure regulator 17 from the delivery pipe 16 and flows back to a fuel tank (not shown).

A water temperature sensor 21 is attached to a water jacket 22 formed on the engine body to detect the cooling water temperature, and a rotation angle sensor 23 is provided near the crankshaft 24 to detect the engine rotation speed. Starter switch 25 is for starting starter 26.

As is conventionally known, the electronic control unit (ECU) 30 includes a central processing unit (MPU) 31, a read-only memory (ROM) 32, a random access memory (RAM) 33, a clock pulse generation circuit (CLOCK) 34, and an input/output circuit. (I/O) port 35,
36 and an A/D converter (ADC) 37, which are interconnected by a bus 38 and an I/D converter (ADC) 37.
A drive circuit 39 is connected to the O port 36. The output signals of the starter switch 25 and rotation angle sensor 23 are stored in the RAM 33 via the I/O port 35, and the output signals of the water temperature sensor 21 and air flow meter 13 are A/D converted by the ADC 37 and stored in the RAM 33. Ru. Based on these output signals, the MPU 31 determines the fuel injection timing and injection time according to the program stored in the ROM 32, and controls the fuel injection valve 15 via the drive circuit 39.
Control opening and closing.

3 to 6 show flowcharts of control programs executed by the ECU 30.

FIG. 3 shows an initial set routine, and this program is executed at the beginning of the main routine shown in FIG. 4 when the engine is started. In step 101, a set temperature is set which will later serve as a reference for determining whether to set the flag XINJ to 1 or 0. In step 102, it is determined whether or not the vehicle is traveling at a high altitude based on the detection signal from a pressure sensor, etc. If the determination is affirmative, a predetermined value A is subtracted from the set temperature in step 103, and if the determination is negative, step 103 is skipped. do. That is, in the case of highlands, the fuel pressure is slightly lower than in the case of flatlands, but the air density decreases, which lowers the idle speed, making rough idle or stall more likely to occur, so the set temperature is set low.

Next, in step 104, the value of the cooling water temperature obtained from the output signal of the water temperature sensor 21 is read, and in step 105, it is determined whether this water temperature is higher than the set temperature. If the water temperature is higher than the set temperature, the flag XINJ is set to 0 to prevent asynchronous injection as described later, and if the water temperature is lower than the set temperature, the flag stipulated in

At step 108, a flag XASY indicating whether steps 205 and 206 of the main routine shown in FIG. 4, ie, the step for executing asynchronous injection, have been executed is set to 0. Then, in step 109, other initial settings are made, and this program is ended.

FIG. 4 shows the main routine. Step 20
1, the initial set routine shown in FIG. 3 is executed and the flag XINJ is set to 0 or 1. In step 202, it is determined whether the starter switch 25 is ON or not, and if the determination is negative, steps 203 to 2 are performed.
07 is skipped, but if the determination is affirmative, step 203 is executed to determine whether 100 msec has passed since the starter switch 25 was turned on.
Until 100 msec has elapsed, there may be noise in the starter switch ON signal shown in Figure 7.
In order to avoid being affected by this noise, steps 204 to 207 are skipped and asynchronous injection is not performed. Conversely, if 100 msec has elapsed, steps 204 and subsequent steps are executed, and asynchronous injection is performed as necessary.

In step 204, it is determined whether the flag XASY is 0 or not. When the flag XASY is 1, steps 205, 206, and 207 have already been executed to perform asynchronous injection, so these steps are skipped, and when the flag XASY is 0, the process proceeds to steps 205 and below. In step 205, the flag XINJ determined in the routine of FIG. 3 is 1 or 0.
Determine whether If the flag XINJ is 1, as mentioned above, the water temperature is low and there is no risk of the fuel in the fuel injection valve 15 boiling under reduced pressure, so step 206 is executed and fuel is injected for approximately 9 msec (i.e., asynchronous injection). (denoted by P in FIG. 7). Flag XINJ is 0 in step 205
If so, the water temperature is high and there is a risk that the fuel in the fuel injection valve 15 will boil under reduced pressure, so step 206 is skipped and asynchronous injection is not performed.

Next, in step 207, the flag XASY is set to 1. This flag XASY is
Alternatively, it indicates that steps 205 and 206 have been executed, that is, the step of determining whether or not to perform asynchronous injection has been executed. Therefore, if this flag XASY is set to 1, then step 2
If the process returns to step 02 and steps 202 and subsequent steps are executed, a negative determination is made in step 204, and steps 205 to 207 are skipped. In other words,
When the flag XASY is 1, asynchronous injection is no longer performed and normal synchronous injection is performed.

5 and 6 show a flowchart of a program for performing synchronous injection.

The program shown in FIG. 5 is interrupted every 30° crank angle. In step 301, it is determined whether or not it is the fuel injection timing, more specifically, whether the pulse signal indicating the 30° crank angle is closest to the fuel injection timing, and if a negative determination is made, the following steps are not executed. , if the judgment is affirmative, step 302
-304 are executed. In step 302, the basic injection time amount τ _p is determined from Q/NXK. Here, Q is the intake air amount, N is the engine speed, and K is the coefficient. This basic injection time is corrected in step 303 by a correction coefficient such as an air-fuel ratio correction coefficient, that is, the actual injection time TAU=τ _p ×α+
β is calculated. Next, in step 304,
The time from the 30° crank angle pulse signal to the actual injection timing is set in the register included in the drive circuit 39, and this routine is completed.

The program of FIG. 6 is interrupted when the time set in step 304 above is reached. That is, in this program, when the comparison circuit in the drive circuit 39 determines that the current time matches the time set in the register,
executed. That is, in step 401, an injection start command signal is output to the fuel injection valve 15, and in step 402, the injection end time is calculated from the injection time TAU, and this routine is ended.
When the injection end time comes, the drive circuit 39 outputs an injection end command signal to the fuel injection valve 15.

Thus, synchronous injection (indicated by Q in FIG. 7) is performed. This synchronous injection is performed for approximately 1.5 msec.

As described above, this embodiment is configured to stop asynchronous injection at the time of high temperature restart. When asynchronous injection is canceled in this way, the water temperature or the fuel temperature is high, the engine has not been stopped for a long time, and fuel has adhered to the walls of the intake pipe and the like. Therefore, the engine has good startability even without asynchronous injection.

Compared to asynchronous injection for starting, synchronous injection only opens the fuel injection valve for a very short time, so the fuel pressure inside the injection valve does not drop and the fuel does not boil under reduced pressure. .

In addition, instead of setting the flag XINJ to 1 or 0 depending on the cooling water temperature, the flag is set depending on the fuel temperature.
You may also set XINJ.

In addition, there is a water temperature switch that turns on and off depending on the coolant temperature, or a water temperature switch that turns on and off depending on the fuel temperature.
It is also possible to perform asynchronous injection using a fuel temperature switch.

〔Effect of the invention〕

As described above, according to the present invention, there is no risk that the fuel in the fuel injection valve will boil under reduced pressure during a high-temperature restart, and the air-fuel ratio will be prevented from becoming too lean immediately after startup, resulting in rough idling and engine stall. is avoided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the present invention, Fig. 2 is a schematic diagram showing an engine to which an embodiment of the present invention is applied, Fig. 3 is a flowchart showing an initial set routine, and Fig. 4 is a main routine. FIG. 5 is a flowchart showing the 30° crank angle interrupt routine, FIG. 6 is a flowchart showing the time coincidence interrupt routine, and FIG. 7 is a timing chart showing the state of fuel injection at startup. 15...Fuel injection valve, 21...Water temperature sensor (state detection means).

Claims (1)

[Claims] 1. Synchronous injection means for causing the fuel injection valve to perform an injection action at every predetermined crank angle during normal operation, and a synchronous injection means for causing the fuel injection valve to perform an injection action for a longer time than the fuel injection by the synchronous injection means when starting the engine. an asynchronous injection means for causing the asynchronous injection, a state detection means for detecting the engine state, and a start control means for controlling the asynchronous injection means so as not to perform an injection action when there is a possibility that decompression boiling of the fuel may occur depending on the engine state. A fuel injection control device comprising: